Liquid crystal aligning agent and liquid crystal display device employing it

ABSTRACT

To provide a liquid crystal aligning agent useful to obtain a liquid crystal alignment film excellent in liquid crystal alignment properties, alignment controlling power and rubbing resistance, having high voltage retention characteristics and having reduced charge accumulation, and a liquid crystal display device which is less susceptible to display failure, to lowering of contrast or to image persistence. 
     A liquid crystal aligning agent comprising a low resistance polyimide precursor having a volume resistivity of from 1×10 10  to  1×10   14  Ωcm when formed into a film, and a high alignment polyimide precursor or polyimide having a specific structure, and a liquid crystal display device employing this liquid crystal aligning agent.

TECHNICAL FIELD

The present invention relates to a liquid crystal aligning agent to beused for forming a liquid crystal alignment film, and a liquid crystaldisplay device employing it.

BACKGROUND ART

Liquid crystal display devices are presently widely used as displaydevices which can realize thin structure/light weight. The displaycharacteristics of liquid crystal display devices are known to besubstantially influenced by the alignment of liquid crystal, the pretiltangle of liquid crystal, the stability of the pretilt angle, electricalcharacteristics, etc. In order to improve the display characteristics ofsuch liquid crystal display devices, not only the liquid crystalmaterial to be used but also the liquid crystal alignment film whichuniformly aligns the liquid crystal becomes important. If the liquidcrystal alignment film has low liquid crystal alignment properties,image failure may occur, and if the alignment controlling power ofliquid crystal is low, the liquid crystal which has been continuouslydriven will not recover to the initial state, thus causing persistenceof the displayed image. Further, the liquid crystal alignment film alsohas an influence over the voltage retention characteristics and thecharge accumulation characteristics when the liquid crystal is driven.If the voltage retention is low, the contrast on the displayed image maydecrease, and if accumulation of the charge against a DC voltage issignificant, persistence of the displayed image may occur. Further, arubbing treatment is presently commonly carried out for formation of aliquid crystal alignment film. If the rubbing resistance of the liquidcrystal alignment film is low, the film may be separated or the filmsurface may be scraped away by rubbing, which may cause display failure.

In order to solve such problems as peeling of the film by rubbing, theliquid crystal alignment properties and the voltage retentioncharacteristics, a liquid crystal alignment film comprising a mixture ofa polyamic acid having an alkylene structure at the diamine moiety and apolyamic acid having an aliphatic structure at the tetracarboxylic acidmoiety has been proposed (e.g. JP-A-11-264984, JP-A-11-335461). However,characteristics required for a liquid crystal alignment film becomestrict along with an improvement in performance of liquid crystaldisplay devices, and it becomes difficult to satisfy all the requiredcharacteristics only with conventional technique.

DISCLOSURE OF THE INVENTION

Under these circumstances, it is an object of the present invention toprovide a liquid crystal aligning agent to provide a liquid crystalalignment film excellent in liquid crystal alignment properties, liquidcrystal controlling power and rubbing resistance, having high voltageretention characteristics and having reduced charge accumulation, and aliquid crystal display device which hardly causes image failure,decrease in contrast, persistence of the image, etc.

The present inventors have conducted extensive studies to achieve theabove object and as a result, have found the present invention. Namely,the above object has been found to be achieved by a liquid crystalaligning agent comprising a polyimide precursor having a structural unitrepresented by the formula (1) and having a volume resistivity of from1×10¹⁰ to 1×10¹⁴ Ωcm when formed into a film, and a polyimide precursorhaving a structural unit represented by the formula (2-1) or a polyimidehaving a structural unit represented by the formula (2-2), and a liquidcrystal display device employing this liquid crystal aligning agent:

in the formula (1), R represents a hydrogen atom or an alkyl group, Xrepresents a tetravalent organic group, and A represents a bivalentorganic group,

in the formulae (2-1) and (2-2), R represents a hydrogen atom or analkyl group, Y represents a tetravalent organic group, B represents abivalent organic group, and from 10 to 100 mol % of B is a bivalentorganic group having any one of the following structures (3) to (5) inits structure, or a paraphenylene group:

in the formula (3), m₁ is an integer of from 1 to 18,

in the formula (4), one or a plurality of optional hydrogen atoms on thebenzene rings may be substituted by a monovalent organic group otherthan a primary amino group, and m₂ is an integer of from 0 to 8,

in the formula (5), one or a plurality of optional hydrogen atoms on thebenzene rings may be substituted by a monovalent organic group otherthan a primary amino group, and m₃ is an integer of from 1 to 4.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1: a schematic view illustrating a two pixel in-plane switchingcomb electrode used in Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be explained in detail below.

The liquid crystal aligning agent of the present invention is acomposition to be used for formation of a liquid crystal alignment film,and is characterized by comprising a polyimide precursor (hereinafterreferred to as a specific polymer a) as a low resistance componenthaving a structural unit represented by the formula (1) and having avolume resistivity of from 1×10¹⁰ to 1×10¹⁴ Ωcm and a polyimideprecursor as a high alignment component having a structural unitrepresented by the formula (2-1) or a polyimide as a high alignmentcomponent having a structural unit represented by the formula (2-2)(hereinafter referred to as a specific polymer b).

As the contents of the specific polymers a and b, the specific polymer ais contained in an amount of from 10 to 95 wt %, more preferably from 60to 90 wt %, based on the total amount of the specific polymers a and b.Namely, the specific polymer b is contained in an amount of from 90 to 5wt %, more preferably from 40 to 10 wt %, based on the total amount ofthe specific polymers a and b. If the amount of the specific polymer ais too small, the charge accumulation characteristics and the rubbingresistance of the liquid crystal alignment film tend to deteriorate, andif the amount of the specific polymer b is too small, the alignmentproperties and the alignment controlling power of liquid crystal tend todeteriorate. One type or at least two types may be used as each of thespecific polymers a and b to be contained in the liquid crystal aligningagent of the present invention. Further, in order to further improve therubbing resistance of the liquid crystal alignment film, one of X in theformula (1) and Y in the formula (2-1) or (2-2) preferably has analicyclic structure or an aliphatic structure.

Specific polymer a The specific polymer a is a polyimide precursor as alow resistance component, and has a volume resistivity of from 1×10¹⁰ to1×10¹⁴ Ωcm, preferably from 1×10¹² to 1×10¹⁴ Ωcm, more preferably from1×10¹² to 5×10¹³ Ωcm. The volume resistivity is a value represented whenthe polyimide precursor is formed into a film. If the resistivity is toohigh, the image persistence/irregularity due to charge accumulation mayoccur, and if it is too low, the voltage retention characteristics maydeteriorate. The liquid crystal aligning agent of the present inventionis usually coated on a substrate and then baked, and thus the specificpolymer a preferably has the above volume resistivity after baking. Thebaking temperature is from 100 to 350° C., preferably from 150 to 300°C., more preferably from 200 to 250° C., particularly preferably 220° C.

The volume resistivity of the specific polymer a can be confirmed asfollows.

A solution of the specific polymer a is coated on a glass substrateprovided with ITO transparent electrodes by e.g. spin coating, thesolvent is evaporated on a hotplate of about 80° C., and then baking atan aimed temperature is carried out to form a coated film having athickness of about 1 μm. Aluminum is deposited on the surface of thecoated film via a mask to form an upper electrode of from about 0.05 toabout 0.1 cm², whereby a sample for measuring the volume resistivity isobtained. A voltage of 10 V is applied between the ITO electrode and analuminum electrode of this sample, and the current 60 seconds afterapplication of the voltage is measured. The volume resistivity iscalculated from measured values of the current, the area of theelectrode and the film thickness.

In the formula (1), A is a bivalent organic group, and one type or amixture of at least two types may be used. Further, although thestructure is not particularly limited, at least one type is preferably abivalent organic group having a nitrogen atom. The bivalent organicgroup having a nitrogen atom may, for example, be a bivalent organicgroup having a cyclic structure containing a nitrogen atom, such as apyridine ring, a pyrimidine ring, a triazine ring, a piperidine ring ora piperazine ring, or a bivalent organic group having anitrogen-containing group such as a secondary or higher amino group, anamide group or a urea group. Among these bivalent organic groups havinga nitrogen atom, particularly preferred is a bivalent organic grouphaving one of the following structures (6) and (7):

In the formula (6), p is an integer of from 1 to 5, and in view of thealignment properties of liquid crystal, p is preferably 1, and morepreferred is a diphenylamine group having bonds at 4,4′-positions.

The structure of the formula (7) is preferably a carbazole group havingbonds at 3,6-positions in view of the alignment properties of liquidcrystal.

In the above structure (6) or (7), one or a plurality of optionalhydrogen atoms in the benzene rings may be substituted by a monovalentorganic group other than a primary amino group. Such a monovalentorganic group may, for example, be a C₁₋₂₀ alkyl group, a C₂₋₂₀ alkenylgroup, a C₁₋₂₀ alkoxy group, a C₁₋₂₀ fluorine-containing alkyl group, aC₂₋₂₀ fluorine-containing alkenyl group, a C₁₋₂₀ fluorine-containingalkoxy group, a cyclohexyl group, a phenyl group, a fluorine atom or agroup comprising a combination thereof. In view of the alignmentproperties of liquid crystal, it is preferably a monovalent organicgroup selected from the group consisting of a C₁₋₄ alkyl group, a C₂₋₄alkenyl group, a C₁₋₄ alkoxy group, a C₁₋₄ fluorine-containing alkylgroup, a C₂₋₄ fluorine-containing alkenyl group and a C₁₋₄fluorine-containing alkoxy group. The more preferred structure (6) or(7) is one having no hydrogen atoms on the benzene rings substituted.

In A in the formula (1), the proportion of A having a nitrogen atom ispreferably from 10 to 100 mol %, more preferably from 60 to 100 mol %.When the proportion of A having a nitrogen atom is at least 10 mol %,the volume resistivity can be effectively lowered, and a polyimideprecursor having an aimed volume resistivity can easily be obtained.Particularly in the case of the structure (6) or (7), the polyimideprecursor will have not only a moderate volume resistivity but also hasfavorable voltage retention characteristics, and further, excellentcharge accumulation characteristics and rubbing resistance will beimparted to the liquid crystal alignment film.

Further, for A in the formula (1), a bivalent organic group having asubstituent known to have an effect to increase the tilt angle, such asa long-chain alkyl group, a perfluoroalkyl group or a steroid skeletongroup, may be present for the purpose of increasing the pretilt angle ofliquid crystal.

X in the formula (1) is a tetravalent organic group, and one type or atleast two types may be present. The structure is not particularlylimited, but at least one type is preferably a tetravalent organic grouphaving an alicyclic structure or a tetravalent organic group having analiphatic structure with a view to obtaining high voltage retentioncharacteristics and rubbing resistance. In such a case, proportion ofthe tetravalent organic group having an alicyclic structure or thetetravalent organic group having an aliphatic structure in X ispreferably from 20 to 100 mol %, more preferably from 50 to 100 mol %.The tetravalent organic group having an alicyclic structure ispreferably a structure having four carboxylic acids removed from atetracarboxylic acid such as 1,2,3,4-cyclobutanetetracarboxylic acid,2,3,5-tricarboxycyclopentylacetic acid,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid orbicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic acid. The tetravalentorganic group having an aliphatic structure is preferably a structurehaving four carboxylic acids removed from 1,2,3,4-butanetetracarboxylicacid.

Further, when X in the formula (1) is a structure having four carboxylicacids removed from e.g. pyromeritic acid,3,3′,4,4′-biphenyltetracarboxylic acid,3,3′,4,4′-benzophenonetetracarboxylic acid or1,4,5,8-naphthalenetetracarboxylic acid, although the voltage retentioncharacteristics tend to decrease, there are such effects that thealignment properties of the liquid crystal are excellent, and thataccumulation of the charge is further reduced. Accordingly, whenimprovement in the alignment properties of the liquid crystal andfurther reduction of accumulation of the charge are important, X may besuch a tetravalent organic group, or such a tetravalent organic groupmay be present as part of X.

In the formula (1), R is a hydrogen atom or an alkyl group and is notparticularly limited. Specifically, the alkyl group may, for example, bea methyl group, an ethyl group, a n-propyl group or an iso-propyl group.

The method to obtain the polyimide precursor having a structural unitrepresented by the formula (1) is not particularly limited. In general,the polyimide precursor (polyamic acid) wherein R in the formula is ahydrogen atom can be obtained by a reaction of a tetracarboxylicdianhydride to constitute X in the formula (1) with a diamine toconstitute A in the formula (1), and this method is preferably employedalso to obtain the specific polymer a. Further, the polyimide precursor(polyamic acid alkyl ester) wherein R in the formula is an alkyl groupcan be obtained by dehydration concentration of the above polyamic acidwith an alcohol such as methanol, ethanol, 1-propanol or 2-propanol, orby reaction of a tetracarboxylic dianhydride to constitute X in theformula (1) with an alcohol such as methanol, ethanol, 1-propanol or2-propanol to obtain a tetracarboxylic acid diester, followed bydehydration condensation with a diamine to constitute A in the formula(1).

In order to obtain a polyimide precursor in which a plurality of X's arepresent in a specific proportion, or in order to obtain a polyimideprecursor in which a plurality of A's are present in a specificproportion, tetracarboxylic dianhydrides to constitute X's or diaminesto constitute A's each in an aimed proportion are used and reacted. Forexample, in order that the proportion of A having a nitrogen atom in thepolyimide precursor is 10 mol %, the proportion of a diamine toconstitute A having a nitrogen atom to the total amount of diamines tobe used for preparation of the polyimide precursor should be adjusted to10 mol %. Likewise, in order that the proportion of X having analicyclic structure in the polyimide precursor is 20 mol %, theproportion of a tetracarboxylic dianhydride to constitute X having analicyclic structure to the total amount of tetracarboxylic dianhydridesto be used for preparation of the polyimide precursor should be adjustedto 20 mol %.

Specific examples of the diamine to constitute A in the formula (1) areshown below, but the diamine is not limited thereto.

As diamines to constitute A having a nitrogen atom, 2,3-diaminopyridine,2,6-diaminopyridine, 3,4-diaminopyridine, 2,4-diaminopyrimidine,2,4-diamino-6-hydroxypyrimidine, 2,4-diamino-1,3,5-triazine,2,4-diamino-1,3,5-triazine, 2,4-diamino-6-isopropoxy-1,3,5-triazine,2,4-diamino-6-methoxy-1,3,5-triazine,2,4-diamino-6-phenyl-1,3,5-triazine, 2,6-diaminopurine,1,4-bis(3-aminopropyl)piperazine, 2,4-diamino-5-phenylthiazole,3,5-diamino-1,2,4-triazole, 3,6-diaminoacridine, acrinol,2,5-bis(4-aminophenyl)-1,3,4-oxadiazole, diethylenetriamine,triethylenetetramine, 3,3-diamino-dipropylamine, pentaethylenehexamine,N,N-bis(3-aminopropyl)methylamine, 4,4′-diaminobenzanilide,2,6-diamino-4-nitrotoluene, N,N′-bis(4-aminophenyl)-N-phenylamine,N,N′-bis(4-aminophenyl)-N-methylamine and 4,4′-diaminodiphenylurea, may,for example, be mentioned.

As a diamine to constitute A containing one of the structures (6) and(7), a diamine having the following structure (8) or (9) may bementioned:

wherein q is an integer of from 1 to 5,

In the above structures (8) and (9), one or a plurality of optionalhydrogen atoms on the benzene rings may be substituted by a monovalentorganic group other than a primary amino group. Such a monovalentorganic group may, for example, be a C₁₋₂₀ alkyl group, a C₂₋₂₀ alkenylgroup, a C₁₋₂₀ alkoxy group, a C₁₋₂₀ fluorine-containing alkyl group, aC₂₋₂₀ fluorine-containing alkenyl group, a C₁₋₂₀ fluorine-containingalkoxy group, a cyclohexyl group, a phenyl group, a fluorine atom or agroup comprising a combination thereof. In view of the alignmentproperties of liquid crystal, it is preferably a monovalent organicgroup selected from a C₁₋₄ alkyl group, a C₂₋₄ alkenyl group, a C₁₋₄alkoxy group, a C₁₋₄ fluorine-containing alkyl group, a C₂₋₄fluorine-containing alkenyl group and a C₁₋₄ fluorine-containing alkoxygroup. The more preferred structure (8) or (9) is one having no hydrogenatoms on the benzene rings substituted.

The diamine having the structure (8) or (9) is particularly preferably4,4′-diaminodiphenylamine or 3,6-diaminocarbazole in view of reactivitywith a tetracarboxylic dianhydride and the liquid crystal alignmentproperties when formed into an alignment film.

The diamine mentioned in the above specific examples is preferred as amaterial to prepare the specific polymer a, and a polyimide precursorhaving a structural unit represented by the formula (1), prepared byusing such a diamine in an amount of preferably from 10 to 100 mol %,more preferably from 60 to 100 mol %, among diamines to be used for thereaction with a tetracarboxylic dianhydride, is preferred as thespecific polymer a.

In addition, specific examples of the diamine to constitute A are shownbelow, but the diamine is not limited thereto.

As examples of an aliphatic diamine, diaminomethane, 1,2-diaminoethane,1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane,1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane,1,10-diaminodecane, 1,3-diamino-2,2-dimethylpropane,1,4-diamino-2,2-dimethylbutane, 1,6-diamino-2,5-dimethylhexane,1,7-diamino-2,5-dimethylheptane, 1,7-diamino-4,4-dimethylheptane,1,7-diamino-3-methylheptane, 1,9-diamino-5-methylnonane,2,11-diaminododecane, 1,12-diaminooctadecane and1,2-bis(3-aminopropoxy)ethane may be mentioned.

As examples of an alicyclic diamine, 1,4-diaminocyclohexane,1,3-diaminocyclohexane, 4,4-diaminodicyclohexylmethane,4,4-diamino-3,3′-dimethyldicyclohexylmethane and isophorone diamine maybe mentioned.

As examples of a carbon ring type aromatic diamine, o-phenylenediamine,m-phenylenediamine, p-phenylenediamine, a diaminotoluene (such as2,4-diaminotoluene), 1,4-diamino-2-methoxybenzene, 2,5-diaminoxylene,1,3-diamino-4-chlorobenzene, 1,4-diamino-2,5-dichlorobenzene,1,4-diamino-4-isopropylbenzene, 4,4′-diaminodiphenyl-2,2′-propane,4,4′-diaminodiphenylmethane, 2,2′-diaminostilbene, 4,4′-diaminostilbene,4,4′-diaminodiphenyl ether, 4,4-diphenyl thioether,4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone, phenyl4,4′-diaminobenzoic acid phenyl ether, 2,2′-diaminobenzophenone,4,4-diaminobenzyl, bis(4-aminophenyl)phosphine oxide,bis(3-aminophenyl)methylsulfine oxide, bis(4-aminophenyl)phenylphosphineoxide, bis(4-aminophenyl)cyclohexylphosphine oxide,1,8-diaminonaphthalene, 1,5-diaminonaphthalene,1,5-diaminoanthraquinone, diaminofluorene,bis(4-aminophenyl)diethylsilane, bis(4-aminophenyl)dimethylsilane,bis(4-aminophenyl)tetramethyldicyloxane, 3,4′-diaminodiphenyl ether,benzidine, 2,2′-dimethylbenzidine,2,2-bis[4-(4-aminophenoxy)phenyl]propane,bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4′-bis(4-aminophenoxy)biphenyl,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,1,4-bis(4-aminophenoxy)benzene and 1,3-bis(4-aminophenoxy)benzene may bementioned.

As a diamine to constitute A which increases the pretilt angle of liquidcrystal, 1-dodecyloxy-2,4-diaminobenzene,1-hexadecyloxy-2,4-diaminobenzene, 1-octadecyloxy-2,4-diaminobenzene,1,1-bis(4-aminophenyl)cyclohexane,2,2-bis[4-(4-aminophenoxy)phenyl]octane, 4,4′-diamino-3-dodecyl diphenylether, 4-(4-trans-n-heptylcyclohexylphenoxy)-1,3-diaminobenzene,4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene and4-trans-n-pentylbicyclohexyl-3,5-diaminobenzoate may, for example, bementioned.

Specific examples of the tetracarboxylic dianhydride to constitute X inthe formula (1) are shown below, but the tetracarboxylic dianhydride isnot limited thereto.

As a tetracarboxylic dianhydride to constitute X having an alicyclicstructure, 1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic dianhydride,1,2,3,4-cyclopentanetetracarboxylic dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic dianhydride,1,2,4,5-cyclohexanetetracarboxylic dianhydride,2,3,5-tricarboxycyclopentylacetic dianhydride,3,4-dicarboxy-1-cyclohexylsuccinic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride andbicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride may, forexample, be mentioned. As a tetracarboxylic dianhydride to constitute Xhaving an aliphatic structure, 1,2,3,4-butanetetracarboxylic dianhydridemay, for example, be mentioned. Among them, it is particularly preferredto use at least one tetracarboxylic dianhydride selected from the groupconsisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride,2,3,5-tricarboxycyclopentylacetic dianhydride,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride,bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride and1,2,3,4-butanetetracarboxylic dianhydride.

Further, as a tetracarboxylic dianhydride to constitute X, aromatictetracarboxylic dianhydrides such as pyromellitic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride,2,3,3′,4′-benzophenonetetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride,1,2,5,6-naphthalenetetracarboxylic dianhydride,2,3,6,7-naphthalenetetracarboxylic dianhydride and1,4,5,8-naphthalenetetracarboxylic dianhydride may be mentioned. Whenimprovement in alignment properties of liquid crystal and furtherreduction in accumulation of the charge are important, it is preferredto use, among these aromatic tetracarboxylic dianhydrides, at least onetetracarboxylic dianhydride selected from the group consisting ofpyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride and1,4,5,8-naphthalenetetracarboxylic dianhydride.

Specific Polymer b

The specific polymer b is a polyimide precursor (polyamic acid, polyamicacid alkyl ester) as a high alignment component, or a polyimide as ahigh alignment component, and is characterized by having a structuralunit represented by the formula (2-1) or (2-2). A liquid crystalalignment film having such a structure is excellent in liquid crystalalignment properties and liquid crystal controlling power.

In the formula (2-1) or (2-2), B is a bivalent organic group, and onetype or at least two types are present as B, but at least one isrequired to be a bivalent organic group having any one of structures (3)to (5) in its structure, or a paraphenylene group. The proportion of Bhaving such a specific structure in B in the formula (2-1) or (2-2) ispreferably from 10 to 100 mol %, more preferably from 50 to 100 mol %.If this proportion is too low, the liquid crystal alignment propertiesor the liquid crystal controlling power may deteriorate in some cases.The structure of other B to be present together with B having the abovespecific structure is not particularly limited. Further, for B, abivalent organic group having a substituent known to have an effect toincrease the tilt angle, such as a long-chain alkyl group, aperfluoroalkyl group or a steroid skeleton group, may be present for thepurpose of increasing the pretilt angle of liquid crystal.

In the formula (3), m₁ is an integer of from 1 to 18, and in view of thealignment properties and heat resistance of liquid crystal, it ispreferably from 1 to 12, more preferably from 2 to 8. Further, it ispreferred that the bivalent organic group having the formula (3) in itsstructure further contains an aromatic ring. The following structuresmay be mentioned as specific examples, but the structure (3) is notlimited thereto.

In the formulae (10) to (13), m₁ is an integer of from 1 to 18,preferably from 1 to 12, more preferably from 2 to 8.

In the formula (4), m₂ is an integer of from 0 to 8, and in view ofvoltage retention characteristics, it is preferably from 0 to 3, morepreferably from 0 to 2.

In the formula (5), m₃ is an integer of from 1 to 4, and in view ofstability of a polyimide precursor solution or a polyimide solution, itis preferably 1 or 2.

In the structures of the formulae (4), (5) and (10) to (13) and theparaphenylene group, one or a plurality of optional hydrogen atoms onthe benzene ring may be substituted by a monovalent organic group otherthan a primary amino group. Such a monovalent organic group may, forexample, be a C₁₋₂₀ alkyl group, a C₂₋₂₀ alkenyl group, a C₁₋₂₀ alkoxygroup, a C₁₋₂₀ fluorine-containing alkyl group, a C₂₋₂₀fluorine-containing alkenyl group, a C₁₋₂₀ fluorine-containing alkoxygroup, a cyclohexyl group, a phenyl group, a fluorine atom or a groupcomprising a combination thereof. In view of the alignment properties ofliquid crystal, it is preferably a monovalent organic group selectedfrom the group consisting of a C₁₋₄ alkyl group, a C₂₋₄ alkenyl group, aC₁₋₄ alkoxy group, a C₁₋₄ fluorine-containing alkyl group, a C₂₋₄fluorine-containing alkenyl group and a C₁₋₄ fluorine-containing alkoxygroup. The more preferred structure is one having no hydrogen atoms onthe benzene ring substituted.

Y in the formula (2-1) or (2-2) is a tetravalent organic group, and onetype or at least two types may be present. The structure is notparticularly limited, but at least one type is preferably a tetravalentorganic group having an aromatic structure with a view to furtherincreasing the alignment properties of liquid crystal. In such a case,the proportion of the tetravalent organic group having an aromaticstructure in Y is preferably from 20 to 100 mol %, more preferably from50 to 100 mol %. The tetravalent organic group having an aromaticstructure is preferably a structure having four carboxylic acids removedfrom a tetracarboxylic acid such as pyromellitic acid,3,3′,4,4′-biphenyltetracarboxylic acid,3,3′,4,4′-benzophenonetetracarboxylic acid,bis(3,4-dicarboxyphenyl)ether, bis(3,4-dicarboxyphenyl)sulfone or2,3,6,7-naphthalenetetracarboxylic acid.

Further, when Y in the formula (2-1) or (2-2) is a structure having fourcarboxylic acids removed from a tetracarboxylic acid such as1,2,3,4-cyclobutanetetracarboxylic acid,2,3,5-tricarboxycyclopentylacetic acid,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid orbicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic acid, although thealignment properties of liquid crystal tend to decrease, there is suchan effect that the voltage retention characteristics increase.Accordingly, when the voltage retention is important, Y may be such atetravalent organic group, or such a tetravalent organic group may bepresent as part of Y.

R in the formula (2-1) is a hydrogen atom or an alkyl group and is notparticularly limited. Specifically, the alkyl group may, for example, bea methyl group, an ethyl group, a n-propyl group or an iso-propyl group.

The method to obtain the polyimide precursor having a structural unitrepresented by the formula (2-1) is not particularly limited. Ingeneral, the polyimide precursor (polyamic acid) wherein R in theformula is a hydrogen atom can be obtained by reaction of atetracarboxylic dianhydride to constitute Y in the formula (2-1) with adiamine to constitute B in the formula (2-1), and this method can bepreferably used also to obtain the specific polymer b. Further, thepolyimide precursor (polyamic acid alkyl ester) wherein R in the formulais an alkyl group can be obtained by dehydration concentration of theabove polyamic acid with an alcohol such as methanol, ethanol,1-propanol or 2-propanol, or by reaction of a tetracarboxylicdianhydride to constitute Y in the formula (2-1) with an alcohol such asmethanol, ethanol, 1-propanol or 2-propanol to form a tetracarboxylicacid diester, followed by dehydration concentration with a diamine toconstitute B in the formula (2-1).

The polyimide having a structural unit represented by the formula (2-2)can be obtained by ring-closure imidation of the polyimide precursorhaving a structural unit represented by the formula (2-1). Further, thepolyimide having a structural unit represented by the formula (2-2) hasonly to have a structural unit represented by the formula (2-2) in partof the polymer structure, and not all the polyimide precursor structurecontained in the polymer structure has to be ring-closure imidated.Namely, a polymer in which both the polyimide precursor structure andthe polyimide structure are present is also included.

In order to obtain a polyimide precursor in which a plurality of Y's arepresent in a specific proportion, or in order to obtain a polyimideprecursor in which a plurality of B's are present in a specificproportion, tetracarboxylic dianhydrides to constitute Y or diamines toconstitute B each in an aimed proportion are used and reacted. Forexample, in order that the proportion of B having a specific structurein the polyimide precursor is 10 mol %, the proportion of a diamine toconstitute B having a specific structure to the total amount of diaminesto be used for preparation of the polyimide precursor should be adjustedto 10 mol %. Likewise, in order that the proportion of Y having anaromatic structure in the polyimide precursor is 20 mol %, theproportion of a tetracarboxylic dianhydride to constitute Y having anaromatic structure to the total amount of tetracarboxylic dianhydridesto be used for preparation of the polyimide precursor should be adjustedto 20 mol %. Further, in order to obtain a polyimide in which aplurality of Y's are present in a specific proportion, or in order toobtain a polyimide in which a plurality of B's are present in a specificproportion, the above polyimide precursor is ring-closure imidated.

Specific examples of the diamine to constitute B in the formula (2-1) or(2-2) are shown below, but the diamine is not limited thereto.

A diamine to constitute B having the structure (3) in its structure may,for example, be 1,2-diaminoethane, 1,3-diaminopropane,1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane,1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane or1,10-diaminodecane. As one further containing an aromatic ring, onecorresponding to the formula (10) may, for example, be1,2-bis(4-aminophenyl)ethane, 1,3-bis(4-aminophenyl)propane,1,4-bis(4-aminophenyl)butane, 1,5-bis(4-aminophenyl)pentane,1,6-bis(4-aminophenyl)hexane, 1,7-bis(4-aminophenyl)heptane,1,8-bis(4-aminophenyl)octane, 1,9-bis(4-aminophenyl)nonane or1,10-bis(4-aminophenyl)decane. Likewise, one corresponding to theformula (11) may, for example, be 1,2-bis(4-aminophenoxy)ethane,1,3-bis(4-aminophenoxy)propane, 1,4-bis(4-aminophenoxy)butane,1,5-bis(4-aminophenoxy)pentane, 1,6-bis(4-aminophenoxy)hexane,1,7-bis(4-aminophenoxy)heptane, 1,8-bis(4-aminophenoxy)octane,1,9-bis(4-aminophenoxy)nonane or 1,10-bis(4-aminophenoxy)decane.Likewise, one corresponding to the formula (12) may, for example, bedi(4-aminophenyl)ethane-1,2-dioate, di(4-aminophenyl)propane-1,3-dioate,di(4-aminophenyl)butane-1,4-dioate, di(4-aminophenyl)pentane-1,5-dioate,di(4-aminophenyl)hexane-1,6-dioate, di(4-aminophenyl)heptane-1,7-dioate,di(4-aminophenyl)octane-1,8-dioate, di(4-aminophenyl)nonane-1,9-dioateor di(4-aminophenyl)decane-1,10-dioate. Likewise, one corresponding tothe formula (13) may, for example, be1,2-bis[4-(4-aminophenoxy)phenoxy]ethane,1,3-bis[4-(4-aminophenoxy)phenoxy]propane,1,4-bis[4-(4-aminophenoxy)phenoxy]butane,1,5-bis[4-(4-aminophenoxy)phenoxy]pentane,1,6-bis[4-(4-aminophenoxy)phenoxy]hexane,1,7-bis[4-(4-aminophenoxy)phenoxy]heptane,1,8-bis[4-(4-aminophenoxy)phenoxy]octane,1,9-bis[4-(4-aminophenoxy)phenoxy]nonane or1,10-bis[4-(4-aminophenoxy)phenoxy]decane.

A diamine to constitute B having the structure (4) in its structure may,for example, be 4,4′-diaminodiphenyl ether,1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene,1,3-bis[4-(4-aminophenoxy)phenoxy]benzene or1,4-bis[4-(4-aminophenoxy)phenoxy]benzene.

A diamine to constitute B having the structure (5) in its structure may,for example, be 4,4′-diaminobenzidine or 4,4′-diamino-p-terphenyl.

A diamine to constitute B which is paraphenylene may, for example, be1,4-diaminobenzene.

The diamines mentioned in the above specific examples is preferred as amaterial to prepare the specific polymer b, and a polyamide precursorhaving a structural unit represented by the formula (2-1), prepared byusing such a diamine in an amount of preferably from 10 to 100 mol %,more preferably from 50 to 100 mol %, among diamines to be used for thereaction with a tetracarboxylic dianhydride, or a polyimide having astructural unit represented by the formula (2-2) prepared similarly, ispreferred as the specific polymer b.

In addition, specific examples of a diamine to constitute B other thanthe specific structure are shown below, but the diamine is not limitedthereto.

As examples of an alicyclic diamine, 1,4-diaminocyclohexane,1,3-diaminocyclohexane, 4,4-diaminodicyclohexylmethane,4,4′-diamino-3,3-dimethyldicyclohexylamine and isophoronediamine may bementioned.

As examples of a carbon ring type aromatic diamine, o-phenylenediamine,m-phenylenediamine, 2,4-diaminotoluene, 1,3-diamino-4-chlorobenzene,4,4′-diaminodiphenyl-2,2′-propane, 4,4′-diaminodiphenylmethane,2,2′-diaminostilbene, 4,4′-diaminostilbene, 4,4′-diphenyl thioether,4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone,4,4′-diaminobenzoic acid phenyl ester, 2,2′-diaminobenzophenone,4,4-diaminobenzyl, bis(4-aminophenyl)phosphine oxide,bis(3-aminophenyl)methylsulfine oxide, bis(4-aminophenyl)phenylphosphineoxide, bis(4-aminophenyl)cyclohexylphosphine oxide,1,8-diaminonaphthalene, 1,5-diaminonaphthalene,1,5-diaminoanthraquinone, diaminofluorene,bis(4-aminophenyl)diethylsilane, bis(4-aminophenyl)dimethylsilane,bis(4-aminophenyl)tetramethyldisiloxane, 3,4′-diaminodiphenyl ether,2,2-bis[4-(4-aminophenoxy)phenyl]propane,bis[4-(4-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,1,4-bis(4-aminophenoxy)benzene and 1,3-bis(4-aminophenoxy)benzene may bementioned.

As examples of a diamine containing a nitrogen atom in addition to thetwo amino groups, 2,4-diaminodiphenylamine, 2,4-diaminopyridine,2,4-diamino-s-triazine, 2,7-diaminodibenzofuran,3,7-diaminophenothiazine, 2,5-diamino-1,3,4-thiadiazole,2,4-diamino-6-phenyl-s-triazine, N,N′-bis(4-aminophenyl)-N-phenylamine,N,N′-bis(4-aminephenyl)-N-methylamine and 4,4′-diaminodiphenylurea maybe mentioned.

As examples of a diamine to constitute B to increase the pretilt angleof liquid crystal, 1-dodecyloxy-2,4-diaminobenzene,1-hexadecyloxy-2,4-diaminobenzene, 1-octadecyloxy-2,4-diaminobenzene,1,1-bis(4-aminophenyl)cyclohexane,2,2-bis[4-(4-aminophenoxy)phenyl]octane, 4,4′-diamino-3-dodecyl diphenylether, 4-(4-trans-n-heptylcyclohexylphenoxy)-1,3-diaminobenzene,4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene and4-trans-n-pentylbicyclohexyl-3,5-diaminobenzoate may be mentioned.

Preparation of Polyamic Acid

In order to obtain a polyamic acid to be used for the specific polymer aor the specific polymer b by a reaction of a tetracarboxylic dianhydridewith a diamine, a simple method is to mix a tetracarboxylic dianhydrideand a diamine and allow them to react with each other in an organicsolvent.

The organic solvent to be used for the above reaction is notparticularly limited so long as it is capable of dissolving the formedpolyamic acid. However, specific examples may be N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam,dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone,hexamethylsulfoxide and γ-butyrolactone. These solvents may be usedalone or as mixed. Further, even a solvent which is incapable ofdissolving the polyamic acid may be used as mixed to the above solventwithin a range not to precipitate the formed polyamic acid. Further,moisture in the organic solvent tends to impair the polymerizationreaction and further may cause hydrolysis of the formed polyamic acid,and therefore, it is preferred to use the organic solvent as dehydratedand dried.

The method for mixing the tetracarboxylic dianhydride component and thediamine component in an organic solvent, may, for example, be a methodwherein a solution having the diamine component dispersed or dissolvedin an organic solvent, is stirred, and the tetracarboxylic dianhydridecomponent is added as it is or as dispersed or dissolved in an organicsolvent, or a method wherein, inversely, the diamine component is addedto a solution having the tetracarboxylic dianhydride component dispersedor dissolved in an organic solvent, or a method wherein thetetracarboxylic dianhydride component and the diamine component arealternately added. In the present invention, either one of these methodsmay be employed. Further, in a case where the tetracarboxylicdianhydride component or the diamine component is made of a plurality ofcompounds, such a plurality of compounds may be reacted in apreliminarily mixed state or may individually sequentially be reacted.

The temperature at the time of reacting the tetracarboxylic dianhydridecomponent and the diamine component in an organic solvent, is usuallyfrom 0 to 150° C., preferably from 5 to 100° C., more preferably from 10to 80° C. The higher the temperature is, the quicker the polymerizationreaction finishes. However, if it is too high, a polymer having a highmolecular weight may not sometimes be obtained. Further, the reactionmay be carried out at an optional concentration, but if theconcentration is too low, it tends to be difficult to obtain a polymerhaving a high molecular weight, and if the concentration is too high,the viscosity of the reaction solution tends to be too high to carry outuniform stirring. Accordingly, it is preferably from 1 to 50 wt %, morepreferably from 5 to 30 wt %. At the initial stage, the reaction may becarried out at a high concentration and then, an organic solvent may beadded.

The ratio of the tetracarboxylic dianhydride component:the diaminecomponent, to be used for the polymerization reaction for the polyamicacid is preferably from 1:0.8 to 1.2 by molar ratio. Further, a polyamicacid obtained in excess of the diamine component, may increasecoloration of the solution, and thus when too much coloration of thesolution is undesirable, the above ratio should be 1:0.8 to 1. Like in ausual polycondensation reaction, the closer the molar ratio to 1:1, thelarger the molecular weight of the polyamic acid to be obtained. If themolecular weight of the polyamic acid is too small, the strength of thecoated film thereby obtainable may sometimes be inadequate, andinversely, if the molecular weight of the polyamic acid is too large,the solution viscosity of a coating solution obtained from the liquidcrystal aligning agent tends to be too high, whereby the operationefficiency at the time of forming a coated film or the uniformity of thecoated film tends to be poor. Therefore, the reduced viscosity (at aconcentration of 0.5 dl/g in NMP at 30° C.) of the polyamic acid to beused for the liquid crystal aligning agent of the present invention ispreferably from 0.1 to 2.0, more preferably from 0.2 to 1.5. From thesimilar reasons, the reduced viscosity of the polyimide precursor or thepolyimide to be used for the liquid crystal aligning agent of thepresent invention is preferably from 0.1 to 2.0 (at a concentration of0.5 dl/g in NMP at 30° C.), more preferably from 0.2 to 1.5.

In a case where it is desirable not to have the solvent used for thepolymerization of the polyamic acid incorporated in the liquid crystalaligning agent of the present invention or in a case where it isdesirable to remove an unreacted monomer component or impurities presentin the reaction solution, the polyamic acid is recovered byprecipitation and purified. A simple method is to put the polyamic acidsolution into a poor solvent under stirring to precipitate and recoverthe polyamic acid. The poor solvent to be used for the precipitation andrecovery of the polyamic acid is not particularly limited, and it may,for example, be methanol, acetone, hexane, butylcellosolve, heptane,methyl ethyl ketone, methyl isobutyl ketone, ethanol, toluene orbenzene. The polyamic acid precipitated by being put into the poorsolvent, may be recovered by filtration and washing and then dried underatmospheric pressure or reduced pressure at room temperature or underheating, to obtain a powder. The polyamic acid may be purified byrepeating an operation of further dissolving this powder in a goodsolvent, followed by reprecipitation, from 2 to 10 times. In a casewhere impurities can not be removed by a single operation of recovery byprecipitation, it is preferred to carry out such a purification step. Itis preferred to use, as the poor solvent, at least three types of poorsolvents such as alcohols, ketones or hydrocarbons, since it is therebypossible to further increase the efficiency for purification. The aboveoperation of recovery by precipitation and purification can be similarlycarried out for the preparation of a polyamic acid alkyl ester or apolyimide as described hereinafter.

Preparation of Polyamic Acid Alkyl Ester

In order to obtain a polyamic acid alkyl ester to be used for thespecific polymer a or the specific polymer b, a simple method is toconvert the above-obtained polyamic acid into a form of an acid chloridewith e.g. thionyl chloride, and condensing the acid chloride with analcohol such as methanol, ethanol, 1-propanol or 2-propanol. Anothermethod may, for example, be a method of using a dehydrating agent suchas dicyclocarbodiimide to prepare a polyisoimide from the above-obtainedpolyamic acid, and reacting the polyisoimide with the above alcohol.Otherwise, a tetracarboxylic dianhydride is reacted with an alcohol suchas methanol, ethanol, 1-propanol or 2-propanol to obtain atetracarboxylic acid diester, which is dehydrocondensed with a diamineusing a phosphorus condensation agent or a condensation agent such ascarbonyl diimidazole.

Preparation of Polyimide

In order to obtain a polyimide to be used for the specific polymer b, asimple method is to subject a polyamic acid having a structural unitrepresented by the formula (2-1) to cyclodehydration. The imidationreaction is usually thermal imidation wherein the solution of thepolyamic acid is heated as it is, or chemical imidation wherein acatalyst is added to the solution of the polyamic acid. However, thechemical imidation wherein the imidation reaction proceeds at arelatively low temperature, is preferred, since decrease in themolecular weight of the polyimide to be obtained, is less likely tooccur.

The chemical imidation can be carried out by stirring the polyamic acidin an organic solvent in the presence of a basic catalyst and an acidanhydride. The reaction temperature at that time is usually from −20 to250° C., preferably from 0 to 180° C., and the reaction time may be from1 to 100 hours. The amount of the basic catalyst is from 0.5 to 30 mols,preferably from 2 to 20 mols, per mol of the amic acid groups, and theamount of the acid anhydride is from 1 to 50 mols, preferably from 3 to30 mols, per mol of amic acid groups. If the amount of the basiccatalyst or the acid anhydride is too small, the reaction may notadequately proceed, and if it is too much, it tends to be difficult tocompletely remove it after completion of the reaction. As the basiccatalyst to be used at that time, pyridine, triethylamine,trimethylamine, tributylamine or trioctylamine may, for example, bementioned, and among them, pyridine is preferred since it has a properbasicity to let the reaction proceed. Whereas, as the acid anhydride,acetic anhydride, trimellitic anhydride or pyromellitic anhydride may,for example, be mentioned, and among them, it is preferred to employacetic anhydride, whereby purification after completion of the reactionwill be easy. As the organic solvent, the above-described solvent to beused for the preparation of the polyamic acid, may be used. Theimidation rate by the chemical imidation may be controlled by adjustingthe amount of the catalyst and the reaction temperature or the reactiontime.

In a polyimide solution thus obtained, the added catalyst still remainsin the solution. Accordingly, in order to use it for the liquid crystalaligning agent of the present invention, it is preferred to precipitateand recover the polymer as described in the preparation of the polyamicacid. The poor solvent and the operation to be used for precipitationand recovery of the polyimide are as described above.

Liquid Crystal Aligning Agent

The liquid crystal aligning agent of the present invention explainedbelow has a form of a coating liquid containing the specific polymer aand the specific polymer b, but may have another form so long as auniform thin film can be formed on a substrate.

In order to obtain a coating liquid containing the specific polymer aand the specific polymer b, reaction solutions of the respectivespecific polymers may be mixed as they are, the specific polymers insolid forms may be dissolved in organic solvents and then mixed, or thespecific polymers in solid forms may be mixed while being dissolved inorganic solvents.

Such an organic solvent is not particularly limited so long as it iscapable of dissolving the resin component to be contained, but specificexamples thereof may be N,N-dimethylformamide, N,N-dimethylacetamide,N-methyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone,N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylsulfoxide,tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide andγ-butyrolactone. These solvents may be used alone or in combination as amixture of a plurality of them.

Further, even a solvent which is incapable of dissolving the resincomponent alone may be mixed to the liquid crystal aligning agent of thepresent invention within a range not to let the resin componentprecipitate. Especially, it has been known that the uniformity of thecoated film at the time of coating on the substrate improves by properlymixing a solvent having a low surface tension, such as ethylcellosolve,butylcellosolve, ethylcarbitol, butylcarbitol, ethylcarbitol acetate,ethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol,1-butoxy-2-propanol, 1-phenoxy-2-propanol, propylene glycol monoacetate,propylene glycol diacetate, propylene glycol-1-monomethylether-2-acetate, propylene glycol-1-monoethyl ether-2-acetate,dipropylene glycol, 2-(2-ethoxypropoxy)propanol, lactic acid methylester, lactic acid ethyl ester, lactic acid n-propyl ester, lactic acidn-butyl ester or lactic acid isoamyl ester, and such an organic solventis suitably used also for the liquid crystal aligning agent of thepresent invention.

The solid content concentration in the coating liquid as the liquidcrystal aligning agent of the present invention may suitably be changeddepending upon the setting of the thickness of the liquid crystalalignment film to be formed, but it is preferably from 1 to 10 wt %. Ifit is less than 1 wt %, it tends to be difficult to form a coated filmwhich is uniform and flawless, and if it is higher than 10 wt %, thestorage stability of the solution may sometimes be poor.

Further, to the liquid crystal aligning agent of the present invention,in order to improve the adhesion of the coated film to the substrate, anadditive such as a silane coupling agent may be added, or other resincomponent may be incorporated.

The liquid crystal aligning agent of the present invention obtained asdescribed above, is subjected to filtration as the case requires, andthen applied to a substrate, followed by drying and baking to form acoated film, and this coated film surface is subjected to alignmenttreatment such as rubbing or irradiation with light, so that it may beused as a liquid crystal alignment film.

As the substrate to be used at that time is not particularly limited solong as it is a highly transparent substrate, and it is possible toemploy a glass substrate or a plastic substrate such as an acrylicsubstrate or a polycarbonate substrate. It is preferred to employ asubstrate having ITO electrodes, etc. formed for liquid crystal drivingwith a view to simplification of the process. Further, in the case of areflection type liquid crystal display device, an opaque material suchas a silicon wafer may be used for a substrate for one side, and for theelectrodes in such a case may be made of a material which reflectslights, such as aluminum.

As the method for applying the liquid crystal aligning agent, a spincoating method, a printing method or an inkjet method may, for example,be mentioned. However, from the viewpoint of the productivity, atransfer printing method is industrially widely employed, and it maysuitably be employed also for the liquid crystal aligning agent of thepresent invention.

The step of drying after application of the liquid crystal aligningagent is not necessarily required, but it is preferred to include adrying step in a case where the time after the application to the bakingis not constant for every substrate or in a case where baking is notimmediately carried out after the application. Such drying may becarried out until the solvent is evaporated to such an extent that thecoated film shape will not be deformed by e.g. transportation of thesubstrate. The drying means is not particularly limited. As a specificexample, a method may be employed wherein drying is carried out for from0.5 to 30 minutes, preferably from 1 to 5 minutes, on a hot plate offrom 50 to 150° C., preferably from 80 to 120° C.

The baking of the liquid crystal aligning agent can be carried out at anoptional temperature of from 100 to 350° C., preferably from 150 to 300°C., further preferably from 200 to 250° C. In a case where a polyimideprecursor is incorporated into the liquid crystal aligning agent, theconversion rate from the polyimide precursor to the polyimide may changedepending upon this baking temperature, but the liquid crystal aligningagent of the present invention is not required to be imidated 100%.However, it is preferred to carry out baking at a temperature higher byat least 10° C., than the heat treatment temperature such as curing of asealing agent, which is required in the step of producing a liquidcrystal cell.

The thickness of the coated film after baking is from 5 to 300 nm,preferably from 10 to 100 nm, since if it is too thick, such will bedisadvantageous from the viewpoint of the power consumption of theliquid crystal display device, and if it is too thin, the reliability ofthe liquid crystal display device may sometimes decrease.

The liquid crystal alignment film obtained from the liquid crystalaligning agent of the present invention as mentioned above, hasexcellent characteristics and thus can be used as a liquid crystalalignment film for e.g. TN, STN, TFT, VA or in-plane switching liquidcrystal display devices and further for ferroelectric orantiferroelectric liquid crystal display devices. Particularly, it issuitably used as a liquid crystal alignment film for an in-planeswitching liquid crystal display device which is susceptible to imagepersistence due to the alignment controlling power.

Liquid Crystal Display Device

The liquid crystal display device of the present invention is oneprepared in such a manner that a substrate provided with a liquidcrystal alignment film is obtained from the liquid crystal aligningagent of the present invention by the above-described method, and then aliquid crystal cell is prepared by a known method to obtain a liquidcrystal display device. As an example for the preparation of a liquidcrystal cell, a method is common wherein a pair of substrates havingliquid crystal alignment films formed thereon are placed with a spacerof from 1 to 30 μm, preferably from 2 to 10 μm, interposed therebetween,so that the rubbing directions will be at an optional angle of from 0 to270°, their periphery is fixed by a sealing agent, then liquid crystalis injected, followed by sealing. The method for sealing liquid crystalis not particularly limited, and it may, for example, be a vacuum methodwherein liquid crystal is injected after reducing the pressure in theliquid crystal cell thus prepared, or a dropping method wherein liquidcrystal is dropped, followed by sealing.

The liquid crystal display device prepared by using the liquid crystalaligning agent of the present invention in such a manner, is excellentin the alignment properties of liquid crystal and alignment controllingpower and has excellent electrical characteristics, and thus can be madeto be a liquid crystal display device which is less susceptible tolowering of contrast or to image persistence. Thus, it is suitablyemployed for display devices of various systems employing nematic liquidcrystal, such as TN, STN, TFT, VA and in-plane switching liquid crystaldisplay devices. Further, by selecting the liquid crystal to be used, itmay be used also for ferroelectric and antiferroelectric liquid crystaldisplay devices. It is particularly preferably used for an in-planeswitching liquid crystal display device which is susceptible to imagepersistence due to the alignment controlling power, among such liquidcrystal display devices.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

EXAMPLES Explanation of Abbreviations Used in the Present ExamplesTetracarboxylic Dianhydrides

-   TC−1: 1,2,3,4-cyclobutanetetracarboxylic dianhydride-   TC−2: 3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic    dianhydride-   TC−3: 1,2,3,4-butanetetracarboxylic dianhydride-   TC−4: bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride-   TC−5: pyromellitic dianhydride

Diamines

-   DA−1: 4,4′-diaminodiphenylamine-   DA−2: 3,6-diaminocarbazole-   DA−3: 4,4-diaminodiphenylmethane-   DA−4: 1,3-bis(4-aminophenoxy)benzene-   DA−5: di(4-aminophenyl)butane-1,4-dioate-   DA−6: 1,5-bis(4-aminophenoxy)pentane-   DA−7: 1,8-bis(4-aminophenoxy)octane-   DA−8: 1,5-bis[4-(4-aminophenoxy)phenoxy]pentane-   DA−9: 1,6-bis[4-(4-aminophenoxy)phenoxy]hexane-   DA−10: 4,4′-diamino-p-terphenyl-   DA−11: paraphenylenediamine-   DA−12: 4,4′-diaminodiphenyl ether-   DA−13: 1,3-diamino-4-octadecyloxybenzene

Organic Solvents

-   NMP: N-methyl-2-pyrrolidone-   GBL: γ-butyrolactone-   BCS: butyl cellosolve

Preparation Examples Preparation of Specific Polymer a PreparationExample 1

18.73 g (0.094 mol) of TC−1 and 19.61 g (0.1 mol) of DA−1 were mixed in345.1 g of NMP and reacted for 5 hours at room temperature to obtain apolyamic acid solution comprising TC−1/DA−1. The polymerization reactionproceeded easily and uniformly, and the reduced viscosity of theobtained polyamic acid was 1.18 dl/g (at a concentration of 0.5 g/dl, inNMP at 30° C.). Further, this solution was diluted so that it comprised5 wt % of the polyamic acid, 75 wt % of NMP and 20 wt % of BCS, toobtain a polyamic acid solution (PA−a1).

This polyamic acid solution (PA−a1) was spin-coated on a glass substrateprovided with ITO transparent electrodes, dried for 5 minutes on ahotplate of 80° C. and then baked for 30 minutes in a hot aircirculation oven at 220° C. to form a coated film having a thickness of1 μm. Then, aluminum was deposited on the surface of the coated film toform an upper electrode (electrode area 0.0707 cm²). A voltage of 10 Vwas applied between the ITO electrode and the aluminum electrode, andthe volume resistivity was calculated from the electric current after 60seconds. As a result, it was 3×10¹² Ωcm.

Preparation Examples 2 to 11

In the same manner as in Preparation Example 1, a tetracarboxylicdianhydride and a diamine were mixed in NMP and reacted for from 5 to 24hours at room temperature, and the obtained solution was diluted withNMP and BCS so that the solution comprised 5 wt % of a polyamic acid, 75wt % of NMP and 20 wt % of BCS, to obtain a polyamic acid solution(PA−a2 to PA−a11). The materials used, and the reduced viscosity and thevolume resistivity of the obtained polyamic acids, including PreparationExample 1, are shown below. The numbers in the brackets representcopolymerization rates.

PA−a1: 1.18 dl/g, 3×10¹² Ωcm, TC−1/DA−1

PA−a2: 1.08 dl/g, 3×10¹² Ωcm, TC−2/DA−1

PA−a3: 0.62 dl/g, 3×10¹² Ωcm, TC−3/DA−1

PA−a4: 0.68 dl/g, 2×10¹² Ωcm, TC−4/DA−1

PA−a5: 1.31 dl/g, 2×10¹² Ωcm, TC−5/DA−1

PA−a6: 1.28 dl/g, 3×10¹² Ωcm, TC−1/DA−2

PA−a7: 1.08 dl/g, 4×10¹³ Ωcm, TC−1/DA−1(60), DA−3(40)

PA−a8: 0.95 dl/g, 3×10¹² Ωcm, TC−1(50), TC−5(50)/DA−1

PA−a9: 1.31 dl/g, 7×10¹² Ωcm, TC−1(80), TC−2(20)/DA-1(80), DA−3(20)

PA−a10: 1.25 dl/g, 4×10¹³ Ωcm, TC−1(80), TC−2(20)/DA-1(60), DA−3(40)

PA−a11: 1.05 dl/g, 2×10¹³ Ωcm, TC−1/DA−1(50), DA-4(50)

Preparation of Specific Polymer b Preparation Example 12

20.07 g (0.092 mol) of TC−5 and 29.23 g (0.1 mol) of DA−4 were mixed in443.7 g of NMP and reacted for 5 hours at room temperature to obtain apolyamic acid solution comprising TC−5/DA−4. The polymerization reactionproceeded easily and uniformly, and the reduced viscosity of theobtained polyamic acid was 0.92 dl/g (at a concentration of 0.5 g/dl, inNMP at 30° C.). Further, this solution was diluted so that it comprised5 wt % of the polyamic acid, 75 wt % of NMP and 20 wt % of BCS, toobtain a polyamic acid solution (PA−b1).

Preparation Examples 13 to 24

In the same manner as in Preparation Example 12, a tetracarboxylicdianhydride and a diamine were mixed in NMP and reacted for from 5 to 24hours at room temperature, and the obtained solution was diluted withNMP and BCS so that the solution comprised 5 wt % of a polyamic acid, 75wt % of NMP and 20 wt % of BCS, to obtain a polyamic acid solution(PA−b2 to PA−b12). The materials used, and the reduced viscosity of theobtained polyamic acids, including Preparation Example 12, are shownbelow. The numbers in the brackets represent copolymerization rates.

PA−b1: 0.92 dl/g, TC−5/DA−4

PA−b2: 1.02 dl/g, TC−5/DA−5

PA−b3: 1.15 dl/g, TC−5/DA−6

PA−b4: 1.07 dl/g, TC−1/DA−6

PA−b5: 0.87 dl/g, TC−1/DA−7

PA−b6: 1.02 dl/g, TC−1/DA−8

PA−b7: 1.00 dl/g, TC−1/DA−9

PA−b8: 1.20 dl/g, TC−1/DA−10

PA−b9: 0.70 dl/g, TC−1/DA−11

PA−b10: 0.69 dl/g, TC−1/DA−6(10), DA−3(90)

PA−b11: 1.04 dl/g, TC−5/DA−6(50), DA−12(50)

PA−b12: 1.05 dl/g, TC−1(50), TC−5(50)/DA−6

Preparation Example 25

29.77 g (0.099 mol) of TC−2 and 28.64 g (0.1 mol) of DA−6 were mixed in330.7 g of NMP and reacted for 5 hours at room temperature to obtain apolyamic acid solution. 100 g of this polyamic acid solution was dilutedwith NMP to 5 wt %, and 26.1 g of acetic anhydride and 12.1 g ofpyridine were added as imidation catalysts and reacted for 3 hours at40° C. This reaction solution was put into 1.2 L of methanol, and theobtained precipitate was collected by filtration, thoroughly washed withmethanol and then dried under reduced pressure at 100° C. to obtain awhite polyimide powder. The reduced viscosity of the obtained polyimidewas 0.9 dl/g. 5 g of this powder was dissolved in 80 g of GBL and 15 gof BCS, to obtain a polyimide solution (PI−b13).

Preparation Example 26

29.77 g (0.099 mol) of TC−2, 8.65 g (0.08 mol) of DA−11 and 7.53 g (0.02mol) of DA−13 were mixed in 260.2 g of NMP and reacted for 10 hours atroom temperature to obtain a polyamic acid solution. 100 g of thispolyamic acid solution was diluted with NMP to 5 wt %, and 24.6 g ofacetic anhydride and 11.4 g of pyridine were added as imidationcatalysts and reacted for 3 hours at 40° C. This reaction solution wasput into 1.2 L of methanol, and the obtained precipitate was collectedby filtration, thoroughly washed with methanol and then dried underreduced pressure at 100° C. to obtain a white polyimide powder. Thereduced viscosity of the obtained polyimide was 0.7 dl/g. 5 g of thispowder was dissolved in 80 g of GBL and 15 g of BCS, to obtain apolyimide solution (PI−b14).

Preparation Example 27

18.63 g (0.095 mol) of TC−1 and 19.83 g (0.1 mol) of DA−3 were mixed in217.9 g of NMP and reacted for 8 hours at room temperature to obtain apolyamic acid solution. The polymerization reaction proceeded easily anduniformly, and the reduced viscosity of the obtained polyamic acid was1.00 dl/g (at a concentration of 0.5 g/dl, in NMP at 30° C.). Further,this solution was diluted so that it comprised 5 wt % of the polyamicacid,

-   75 wt % of NMP and 20 wt % of BCS, to obtain a polyamic acid    solution (PA-1). The volume resistivity of the polyamic acid was    measured in the same manner as in Preparation Example 1, whereupon    it was 2×10¹⁴ Ωcm.

Example 1

The polyamic acid solutions (PA−a1) and (PA−b1) obtained in PreparationExamples were mixed in a weight ratio of 80/20 to obtain a liquidcrystal aligning agent of the present invention.

Using this liquid crystal aligning agent, the rubbing resistance, thevoltage retention characteristics, the charge accumulationcharacteristics, the liquid crystal alignment properties and thealignment controlling power were evaluated.

Evaluation of Rubbing Resistance (Scratches by Rubbing, Scrapes byRubbing)

The liquid crystal aligning agent was spin-coated on a glass substrateprovided with ITO transparent electrodes, dried for 5 minutes on ahotplate of 80° C. and then baked for 30 minutes in a hot aircirculation oven at 220° C. to form a coated film having a thickness of100 nm. This coated surface was subjected to rubbing by means of a rayoncloth by a rubbing apparatus having a roll diameter of 120 mm underconditions of a roll rotational speed of 300 rpm, a roll advancing speedof 20 mm/sec and a pushing amount of 0.5 mm, to obtain a substrateprovided with a liquid crystal alignment film.

The rubbed surface of this substrate provided with a liquid crystalalignment film was observed by a confocal laser microscope, and presenceor absence of scratches on the film surface and adhesion of fragmentsformed by scraping was confirmed. Observation by a confocal lasermicroscope was carried out at a scale of 10 magnifications.

Evaluation of Voltage Retention Characteristics (Voltage Retention)

The liquid crystal aligning agent was spin-coated on a glass substrateprovided with ITO transparent electrodes, dried for 5 minutes on ahotplate of 80° C. and then baked for 30 minutes in a hot aircirculation oven at 220° C. to form a coated film having a thickness of100 nm. This coated surface was subjected to rubbing by means of a rayoncloth by a rubbing apparatus having a roll diameter of 120 mm underconditions of a roll rotational speed of 300 rpm, a roll advancing speedof 20 mm/sec and a pushing amount of 0.5 mm, to obtain a substrateprovided with a liquid crystal alignment film.

Two sheets of such a substrate provided with a liquid crystal alignmentfilm were prepared, a spacer of 6 μm was sprayed on the liquid crystalalignment film surface of one sheet, and then a sealing agent wasprinted thereon, and the other substrate was bonded so that the liquidcrystal alignment film surfaces faced each other and that the rubbingdirections were at right angles, and then, the sealing agent was curedto prepare a void cell. To this void cell, liquid crystal MLC-2003(manufactured by Merck Japan Limited) was injected by a reduced pressureinjection method, and the injection inlet was sealed to obtain a twistednematic liquid crystal cell.

To this twisted nematic liquid crystal cell, a voltage of 4 V wasapplied for 60 μs at a temperature of 23° C., and the voltage after16.67 ms was measured, whereby to what extent the voltage wasmaintained, was calculated as a voltage retention. Further, the samemeasurement was carried out also at a temperature of 90° C.

Evaluation of Charge Accumulation Characteristics (Residual Voltageafter Application of DC Voltage)

Rectangular waves of ±3 V/30 Hz having a DC voltage of 3 V superimposed,were applied to the twisted nematic liquid crystal cell, the voltageretention characteristics of which were measured, and the residualvoltage remaining in the liquid crystal cell immediately after switchingoff the DC 3 V was measured by an optical flicker elimination method.

Evaluation of Liquid Crystal Alignment Properties (Initial Alignment ofAntiparallel Liquid Crystal Cell)

The liquid crystal aligning agent was spin-coated on a glass substrateprovided with ITO transparent electrodes, dried for 5 minutes on ahotplate of 80° C. and then baked for 30 minutes in a hot aircirculation oven at 220° C. to form a coated film having a thickness of100 nm. This coated surface was subjected to rubbing by means of a rayoncloth by a rubbing apparatus having a roll diameter of 120 mm underconditions of a roll rotational speed of 800 rpm, a roll advancing speedof 10 mm/sec and a pushing amount of 0.8 mm, to obtain a substrateprovided with a liquid crystal alignment film.

Two sheets of such a substrate provided with a liquid crystal alignmentfilm were prepared, a spacer of 6 μm was sprayed on the liquid crystalalignment film surface of one sheet, and then a sealing agent wasprinted thereon, and the other substrate was bonded so that the liquidcrystal alignment film surfaces faced each other and that the rubbingdirections made an angle of 180°, and then, the sealing agent was curedto prepare a void cell. To this void cell, liquid crystal MLC-2003(manufactured by Merck Japan Limited) was injected by a reduced pressureinjection method, and the injection inlet was sealed to obtain anantiparallel liquid crystal cell.

This antiparallel liquid crystal cell was interposed between twopolarizing plates which were superposed so that the polarizationdirections intersected with each other, and the alignment state of theliquid crystal was visually observed.

Evaluation of Alignment Controlling Power (AC Driving Image Persistenceof in-Plane Switching Cell)

A liquid crystal aligning agent was spin-coated on a glass substratehaving a two pixel (about 1 cm² per pixel) in-plane switching combelectrode (Cr electrode: electrode width 20 μm, electrode distance 20mm, electrode height 120 nm) as shown in FIG. 1. The liquid crystalaligning agent was dried for 5 minutes on a hotplate of 80° C. and thenbaked for 30 minutes in a hot air circulation oven at 220° C. to form acoated film having a thickness of 100 nm. This coated surface wassubjected to rubbing by means of a rayon cloth by a rubbing apparatushaving a roll diameter of 120 mm under conditions of a roll rotationalspeed of 300 rpm, a roll advancing speed of 20 mm/sec and a pushingamount of 0.5 mm. The rubbing direction was adjusted to make an angle of15° with the direction of the teeth of the comb. Further, a coated filmwas formed in the same manner on a glass substrate having no electrodeformed thereon as a counter substrate, and the coated surface wassubjected to rubbing. The rubbing direction on the glass substratehaving no electrode was adjusted so that after the substrate was bondedto the substrate provided with a comb electrode, the respective rubbingdirections made an angle of 0°.

The above two substrates were employed as a pair, a spacer of 6 μm wassprayed on a liquid crystal alignment film surface of one sheet, andthen a sealing agent was printed thereon, and the other substrate wasbonded so that the liquid crystal alignment film faces faced each otherand that the rubbing directions made an angle of 0°, whereupon thesealing agent was cured to prepare a void cell. To this void cell,liquid crystal MLC-2042 (manufactured by Merck Japan Limited) wasinjected by a reduced pressure injection method, and the injection inletwas sealed to obtain an in-plane switching liquid crystal cell.

Rectangular waves of ±30 V/30 Hz were applied only to one pixel of thein-plane switching liquid crystal cell at a temperature of 60° C. for 3hours. The liquid crystal cell after the voltage was turned off wascooled by air from the fan at room temperature of 23° C. About 10minutes later, the liquid crystal cell which was cooled almost to roomtemperature was interposed between two polarizing plates which weresuperposed so that the polarization directions intersected with eachother, and the contrast between the pixel to which a voltage was appliedand the pixel to which no voltage was applied was visually confirmed.One without difference in color tone between both pixels was rated tohave good alignment controlling power.

Evaluation Results

Results of the above evaluations are shown below.

Rubbing resistance: No scratches nor fragments formed by scraping wereobserved on the surface of the alignment film after rubbing.

Voltage retention characteristics: The voltage retention was 99.0% at23° C. and 85.9% at 90° C.

Charge accumulation characteristics: The residual voltage was 0 V.

Liquid crystal alignment properties: Good. The liquid crystal wasuniformly aligned without flaws.

Alignment controlling power: Good. No difference was observed betweenthe pixel to which a voltage was applied and the pixel to which novoltage was applied.

Examples 2 to 19

The polyamic acid solution and the polyimide solution obtained inPreparation Examples were mixed in the following proportion to obtain aliquid crystal aligning agent of the present invention. Using the liquidcrystal aligning agent, evaluations were carried out in the same manneras in Example 1. The results are shown in Table 1 as describedhereinafter.

Example 2: (PA−a1)/(PA−b5)=70/30

Example 3: (PA−a1)/(PA−b6)=70/30

Example 4: (PA−a1)/(PA−b9)=80/20

Example 5: (PA−a1)/(PA−b11)=80/20

Example 6: (PA−a1)/(PA−b12)=70/30

Example 7: (PA−a2)/(PA−b7)=70/30

Example 8: (PA−a3)/(PA−b8)=70/30

Example 9: (PA−a4)/(PA−b4)=80/20

Example 10: (PA−a5)/(PA−b10)=90/10

Example 11: (PA−a6)/(PA−b3)=80/20

Example 12: (PA−a6)/(PA−b4)=80/20

Example 13: (PA−a7)/(PA−b4)=80/20

Example 14: (PA−a8)/(PA−b2)=90/10

Example 15: (PA−a9)/(PA−b3)=80/20

Example 16: (PA−a10)/(PA−b4)=60/40

Example 17: (PA−a11)/(PA−b9)=70/30

Example 18: (PA−a9)/(PI−b13)=80/20

Example 19: (PA−a9)/(PI−b14)=80/20

TABLE 1 Align- Re- ment Scratched Voltage retention sidual control- or(%) voltage Alignment ling fragments 23° C. 90° C. (V) properties powerby rubbing Ex. 1 99.0 85.9 0 Good Good Nil Ex. 2 98.8 88.5 0 Good GoodNil Ex. 3 98.9 90.2 0 Good Good Nil Ex. 4 99.0 87.0 0 Good Good Nil Ex.5 99.3 88.5 0 Good Good Nil Ex. 6 99.3 91.4 0 Good Good Nil Ex. 7 99.290.3 0 Good Good Nil Ex. 8 99.2 92.1 0 Good Good Nil Ex. 9 98.6 90.1 0Good Good Nil Ex. 10 99.3 88.5 0 Good Good Nil Ex. 11 99.0 90.7 0 GoodGood Nil Ex. 12 98.9 89.1 0 Good Good Nil Ex. 13 99.1 87.3 0 Good GoodNil Ex. 14 99.3 90.6 0 Good Good Nil Ex. 15 98.6 84.8 0 Good Good NilEx. 16 99.1 85.2 0 Good Good Nil Ex. 17 99.0 85.0 0 Good Good Nil Ex. 1899.1 86.2 0 Good Good Nil Ex. 19 99.3 91.7 0 Good Good Nil

Comparative Example 1

The polyamic acid solutions (PA−a1) and (PA-1) obtained in PreparationExamples were mixed in a weight ratio of 80/20 to obtain a liquidcrystal aligning agent for comparison.

Using this liquid crystal aligning agent, the rubbing resistance, thevoltage retention characteristics, the charge accumulationcharacteristics, the liquid crystal alignment properties and thealignment controlling power were evaluated in the same manner as inExample 1. The Results are Shown Below.

Rubbing resistance: No scratches nor fragments by scraping were observedon the surface of the alignment film after rubbing.

Voltage retention characteristics: The voltage retention was 99.2% at23° C. and 91.0% at 90° C.

Charge accumulation characteristics: The residual voltage was 0 V.

Liquid crystal alignment properties: Flow alignment was formed in theform of a fan along the liquid crystal injection direction, and theliquid crystal was not uniformly aligned.

Alignment controlling power: A clear contrast was observed between thepixel to which a voltage was applied and the pixel to which no voltagewas applied, and the liquid crystal at the pixel to which a voltage wasapplied was confirmed not to recover to the original alignment state.

Comparative Example 2

The polyamic acid solutions (PA-1) and (PA−b4) obtained in PreparationExamples were mixed in a weight ratio of 80/20 to obtain a liquidcrystal aligning agent for comparison.

Using this liquid crystal aligning agent, the rubbing resistance, thevoltage retention characteristics, the charge accumulationcharacteristics, the liquid crystal alignment properties and thealignment controlling power were evaluated in the same manner as inExample 1. The results are shown below.

Rubbing resistance: Significant scratches and fragments by scraping wereobserved on the surface of the alignment film after rubbing.

Voltage retention characteristics: The voltage retention was 98.9% at23° C. and 88.2% at 90° C.

Charge accumulation characteristics: The residual voltage was so high as1.7 V.

Liquid crystal alignment properties: The liquid crystal was uniformlyaligned without flaws.

Alignment controlling power: No difference was observed between thepixel to which a voltage was applied and the pixel to which no voltagewas applied.

INDUSTRIAL APPLICABILITY

By using the liquid crystal aligning agent of the present invention, aliquid crystal alignment film excellent in liquid crystal alignmentproperties, alignment controlling power and rubbing resistance, havinghigh voltage retention characteristics and having reduced chargeaccumulation, can be obtained. Further, a liquid crystal display devicehaving a liquid crystal alignment film obtained from the liquid crystalaligning agent of the present invention is excellent in alignmentproperties of liquid crystal and alignment controlling power, and hasexcellent electrical characteristics, whereby it can be made to be aliquid crystal display device which is less susceptible to lowering ofcontrast or to image persistence.

1-7. (canceled) 8: A liquid crystal display device having a liquid crystal alignment film, wherein the liquid crystal alignment film is obtained by subjecting a liquid crystal alignment agent to a rubbing treatment, wherein the liquid crystal alignment agent comprises a polyimide precursor having a structural unit represented by the formula (1) and having a volume resistivity of from 1×10¹⁰ to 1×10¹⁴ Ωcm when formed into a film, and a polyimide precursor having a structural unit represented by the formula (2-1) or a polyimide having a structural unit represented by the formula (2-2):

wherein formula (1), R represents a hydrogen atom or an alkyl group, X represents a tetravalent organic group, and A represents a bivalent organic group, wherein from 10 to 100 mol % of A in formula (1) is a bivalent organic group having the following structure (6) or (7):

wherein formula (6), p is an integer of from 1 to 5,

wherein formulae (2-1) and (2-2), R represents a hydrogen atom or an alkyl group, Y represents a tetravalent organic group, B represents a bivalent organic group, and from 10 to 100 mol % of B is a bivalent organic group having any one of the following structures (3) to (5) in its structure, or a paraphenylene group:

wherein formula (3), m₁ is an integer of from 2 to 18,

wherein formula (4), one or a plurality of optional hydrogen atoms on the benzene rings may be substituted by a monovalent organic group other than a primary amino group, and m₂ is an integer of from 1 to 8,

wherein formula (5), one or a plurality of optional hydrogen atoms on the benzene rings may be substituted by a monovalent organic group other than a primary amino group, and m₃ is an integer of from 1 to
 4. 9: The liquid crystal display device according to claim 8, wherein from 20 to 100 mol % of X in the formula (1) is a tetravalent organic group having an alicyclic structure or a tetravalent organic group having an aliphatic structure. 10: The liquid crystal display device according to claim 8, wherein the polyimide precursor having a structural unit represented by the formula (1) is contained in an amount of from 10 to 95 wt % based on the total amount of said polyamide precursor and the polyimide precursor having a structural unit represented by the formula (2-1) or the polyimide having a structural unit represented by the formula (2-2). 11: The liquid crystal display device according to claim 9, wherein from 20 to 100 mol % of Y in the formula (2-1) or (2-2) is a tetravalent organic group having an aromatic structure. 12: The liquid crystal display device according to claim 9, wherein the polyimide precursor having a structural unit represented by the formula (1) is contained in an amount of from 10 to 95 wt % based on the total amount of said polyamide precursor and the polyimide precursor having a structural unit represented by the formula (2-1) or the polyimide having a structural unit represented by the formula (2-2). 13: The liquid crystal display device according to claim 10, wherein from 20 to 100 mol % of Y in the formula (2-1) or (2-2) is a tetravalent or organic group having an aromatic structure. 14: The liquid crystal display device according to claim 11, wherein the polyimide precursor having a structural unit represented by the formula (1) is contained in an amount of from 10 to 95 wt % based on the total amount of said polyamide precursor and the polyimide precursor having a structural unit represented by the formula (2-1) or the polyimide having a structural unit represented by the formula (2-2). 15: The liquid crystal display device of claim 8, further comprising: a first substrate, and a second substrate, a spacer, wherein the first and second substrate have liquid crystal alignment films formed on at least one surface thereof, wherein the first substrate and the second substrate are separated by the spacer and the liquid crystal alignment films present on the surface of the substrates face one another, and wherein the liquid crystal aligning agent is present in a space formed by the spacer between the first and the second substrates. 